A reduction in fuel consumption of automobile is required from the standpoints of protection of global environment and resource saving. In the gasoline engine used mainly in passenger cars, direct injection of fuel is being pushed forward to improve fuel efficiency.
Conventionally, in a gasoline engine, since fuel injection from suction port has been employed, generation of soot [particulate matter (PM)] has been slight and it has caused little problem. However, in the gasoline engine of fuel direct injection type, generation of PM is more than in the fuel injection from suction port and a measure for not releasing the generated PM into the atmosphere has been needed.
Meanwhile, a honeycomb structure is in use as a trapping filter for removing particulate matter discharged from a diesel engine. As a honeycomb structure used as a trapping filter for particulate matter, there is in use a plugged honeycomb structure having plugging portions at given positions of the two end faces (see, for example, Patent Document 1). Here, the plugged honeycomb structure refers to a honeycomb structure comprising a honeycomb structure body having porous partition walls forming a plurality of divided cells each to function as a passage for fluid (exhaust gas, purified gas) and an outer wall present at the outermost circumference of the honeycomb structure body, and plugging portions provided at “the open ends of given cells at the fluid (exhaust gas) inlet side end face of the honeycomb structure body” as well as at “the open ends of residual cells at the fluid (purified gas) outlet side end face of the honeycomb structure body”. In such a honeycomb structure, an exhaust gas flows into cells from the exhaust gas inlet side end face; the exhaust gas which has flown into the cells passes through partition walls; the exhaust gas (purified gas) which has passed through the partition walls is discharged from the exhaust gas outlet side end face. During the passage of exhaust gas through partition walls, the PM contained in the exhaust gas is captured by partition walls and the exhaust gas turns into a purified gas.
It is considered to use the above-mentioned, plugged honeycomb structure used for removal of the particulate matter discharged from diesel engines, for removal of the particulate matter discharged from gasoline engines.